Conceptual Design Report for the Upgrade of the ALICE ITS

The present document addresses the question of how to improve the ALICE performance for heavy-flavour detection. It will be shown that it is possible to built a new silicon tracker with greatly improved features in terms of determination of the distance of closest approach (dca) to the primary vertex, standalone tracking efficiency at low pt , momentum resolution and readout rate capabilities. This is a consequence of the spectacular progress made in the field of imaging sensors over the last ten years and also the possibility to install a smaller radius beampipe. Moreover, a tracker with the above features creates an opportunity to develop a topological trigger, which can be used in combination with the TRD and TOF detectors for the selection of events containing rare probes. Such a new silicon tracker will allow ALICE to measure charm and beauty production in Pb-Pb collisions with sufficient statistical accuracy down to very low transverse momentum, measure charm baryons and perform precise measurements of beauty production. These measurements are essential in order to understand the energy loss mechanism and thermalization of heavy quarks in the QGP. More in general the proposed upgrade is an important part of the general strategy for the upgrade of the central barrel detectors conceived to deal with high statistics measurments, which will give access to a precise determination of its properties including initial temperature, degrees of freedom, speed of sound, and in general, transport coefficients. This will require running the central barrel detectors with expected Pb–Pb interaction rates of up to 50 kHz, that would provide an accumulated sample of the order of 10 nb−1